Method of making pre-formed single turn magnetic cores



June 1967 e. G. SOMERViLLE 3,

METHOD OF MAKING PRE-FOHMED SINGLE TURN MAGNETIC CORES Filed Oct. 1, 1962 2 Sheets-Sheet l 3mm 27, W7 G. G. SOMERVILLE 3,3273% METHOD OF MAKING FEE-FORMED SINGLE TURN MAGNETIC CORES Filed Oct. 1. 1962 2 Sheets-Sheet 2 United States Patent 3,327,373 METHOD OF MAKING FEE-FORMED SINGLE TURN MAGNETIC (JOKES Gareth G. Somerville, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Filed Oct. 1, 1962, Ser. No. 227,193 3 Claims. Cl. 29-15557) This invention relates to magnetic cores and more particularly to a novel method of making pre-formed single turn magnetic cores.

In the magnetic core art, such as are used in various types of electromagnetic induction apparatus, it is common to use a build of a number of layers of steel laminations, formed to the shape of the desired core. In general, there are two methods which are being used to make such cores. The first method comprises the pre-cutting of a sufficient number of separate laminations of appropriately increasing lengths to form the desired core, stacking the laminations and then forming these laminations into the desired core. The second method generally comprises winding a single strip of magnetic material about a mandrel to form a core having the desired number of laminations. In general, the second type of core is referred to as a spirally wound magnetic core. Regardless of the method used, the magnetic core is subsequently placed about an electromagnetic coil. It has been found desirable in many of the electromagnetic induction apparatus presently being made to pre-form the coil and then to place the core about the coil, generally by means of opening the core to insert it about the coil.

The invention disclosed in this application relates to the method of making a spirally wound magnetic core. In making the spirally wound magnetic core, it is the usual practice to wind the strip of magnetic material on a mandrel, either round or rectangular, and when a round mandrel is used, to subsequently form the core to its desired shape. The core is then cut such that it may be placed about a pre-formed coil member. The core is annealed to relieve the various stresses placed in the core material during its manufacture. The'annealing step may be done either after forming of the core, or after both the forming and cutting of the core. As will be understood, the core may be cut at either one or two points, as desired, to allow it to be later assembled with the pre-formed coil. Where the core is cut at only one point it is usually called a single turn core in that each of the separate laminations extends for approximately a single turn of the core.

In the making of a single turn, pre-formed core by spirally winding the material on a mandrel, a problem usually arises in that when the core is completely wound it is necessary to band the laminations together or else to spot weld the outer lamination to prevent the core from unwinding during the remainder of the core-forming process. A further problem arises during the cutting operation in that if the cutting is done prior to annealing the various laminations tend to loosen and spring out from their wound position, whereas if the cutting is done after the annealing the stresses set up in the core material during cutting are not subsequently relieved, and therefore, tend to increase the core losses of the wound core.

A further problem arising in making the core stems from the fact that it is desirable to provide a core in which all of the joints of the core do not fall in the same area of the core. As is well known, the core joints tend to disturb the magnetic flux flowing in the core, and the joints which are substantially aligned and adjacent to each other tend to increase the disturbance in each of the laminations thereby increasing the overall core losses. It is thus desirable to stagger the various joints in the adjacent laminations so that they will not increase the disturbance of the "ice magnetic flux around the joints of the adjacent laminations. This can be accomplished by cutting each turn or lamination separately in a staggered pattern, in the manner disclosed in Patent 2,960,756. However, this method has the disadvantage that each lamination must be separately cut thus increasing the labor and time required to form the core. Clearly, it is desirable to provide a single cut in the core and still provide the staggered joints in the finished core.

It is, therefore, one object of this invention to provide an improved method of making a pre-formed, single turn magnetic core.

A further object of this invention is to provide an improved method of makin a single cut, single turn mag netic core having staggered joints.

A further object of this invention is to provide a method of making a magnetic core in which the core material is pre-curled or set so as to retain its position on the winding mandrel.

A still further object of this invention is to provide an improved method of making a magnetic core in which only a single cut is made in the core severing the laminations and in which the joint pattern is staggered Within the core.

A still further object of this invention is to provide an improved method of making a magnetic core in which the core material is pro-curled or pre-sct about a winding mandrel and is out prior to annealing of the core.

In carrying out this invention in one form thereof, a strip of magnetic core material is wound about a winding mandrel and is provided with a pre-curl to hold the core material in the desired position about the mandrel. The wound core is then cut along a single plane. The various laminations of the core are then shifted within the core so that the joint in each lamination is staggered with respect to the joints in adjacent laminations. The core is then formed to its desired shape and annealed while in such shape.

The invention which it is desired to protect will be clearly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its objects and advantages are obtained, as well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment of the Referring now to the drawings, in which like numeralsare used to indicate like parts throughout the various views thereof, and referring particularly to FIG. 1 of the drawing, there is shown one form of assembly line which may be used to practice the method of this invention. As shown in FIG. 1, a reel 10 of magnetic strip material 12- is provided for forming the magnetic core. Preferably the magnetic strip material 12 i magnetic material in which the grains of the material are oriented in the lengthwise direction to improve the flux flow therein and hold core losses to a minimum. As will be understood, the orientation of the grains in the lengthwise direction is obtained 'by a grain growth anneal. However, if desired, the magnetic strip material may be used in its semi-processed condition, that is, in a condition in which it is not yet received it grain growth anneal. As will be understood,

when the core is given its stress relief anneal it may also be given a grain growth anneal, if the semi-process magnetic material has been used. The various types of anneal are well known to those skilled in the art and are described, for example, in application Ser. NO. 99,558 filed Mar. 30, 1961, now Patent No. 3,073,722, in the name of Herbert B. Forslund et al., for A Process for Coating Ferrous Material and Material Coated by such Process, and which is assigned to the same assignee as this invention.

As will be understood, regardless of the types of magnetic material used, the method of this invention will be substantially the same, that is, the magnetic material 12 is fed from the payofi? reel to a winding mandrel where the desired number of layers or laminations are spirally wound to form a core of the desired size. The spirally wound laminations are then cut along a single plane through the core. The various laminations are then shifted to provide a series of staggered joints such that the joints in each lamination are staggered in relation to the joint in each of the adjacent laminations. The core with the staggered joints is then formed into the desired core shape and is given a final anneal in such shape. As will be understood, this anneal will relieve all of the stresses which developed in the core material during the winding, cutting and forming operations. Additionally, if semi-processed magnetic material has been used the anneal may also be a grain growth anneal to orient the grains of the material in the lengthwise direction.

In the assembly line shown in FIG. 1, the magnetic material 12 is fed from the reel 10 through the guide rolls 14 and the de-burring mechanism 16. The de-burring mechanism may be driven, for example by means of an electric motor 17. The magnetic material is pulled through the rolls 14 and the de-burring mechanism 16 by means of pull-off rolls 18. As will be understood, the pull-off rolls 18 are driven in any desired manner, for example by means of an electric motor 19 and act to pull the magnetic material 12 off the winding reel 10 through the guide roll 14 and the de-burring mechanism 16. The pull-off rolls 18 also act to feed the magnetic material 12 onto the winding mandrel 20. As will be understood, the winding mandrel 20 may be power driven so as to supply tension to the magnetic material 12 as it is wound about the winding mandrel.

In winding the material 12 about the mandrel 20 it is desired to pre-curl the material 12 so that it will be set in the direction of winding and thereby tend to wrap about the mandrel 20. To provide this pre-curl, a mechanism 22 is provided. As shown, the mechanism 22 comprises a series of forming rolls 24 through which the magnetic material 12 is moved. As will be understood, some of the forming rolls 24 may be driven or reliance may be placed upon the feeding form the pull-off rolls 18 and the tension provided by the power mandrel 20 to pull the material 12 through the forming rolls. The forming rolls 24 apply a continuous curl to the magnetic material 12 in the direction of winding on the mandrel 20. In general, the forming rolls 24 will provide a curl to the magnetic material 12 which is greater than that needed for the diameter of the core material which is already formed upon the mandrel 20. The tension provided on the material 12, due to the driving of mandrel 20, serves to straighten the material 12 thu compensating for the over-curl given to the material by the forming rolls 24 and thus providing the desired curl to material 12 so that it fits snugly about the lower laminations and has no tendency to unwind from the formed core.

The pre-curl mechanism 22 is also provided with a shearing blade or knife 26. The blade 26 may be automatically operated in a known manner to cut material 12 after suflicient laminations have been wrapped about the mandrel 20. One method of operating the shearing blade 26 is by use of a limit switch mechanism 28, mounted on the winding mandrel 20. As shown, the limit switch mechanism 28 rides on the material 12 as the material is wrapped about the mandrel 20. When the core has attained the desired thickness, the limit switch mechanism 28 first acts to open an electrical circuit to stop the rotation of mandrel 20. Then, through a delay mechanism (not shown) the switch 28 closes an electrical circuit causing blade 26 to shear the material 12. Obviously, if desired, other means may be used to automatically operate the blade 26 or it may be manually operated.

After the core has been formed about the winding mandrel 20 and the blade 26 has sheared the strip material, the core may be removed from the winding mandrel 20 and placed in the cutting mechanism 30. As will be understood, inasmuch as the magnetic material 12 has been provided with a pre-curl, it is not necessary to band the wound core nor to spot weld the outer lamination in order to hold the core material in the desired wound position. In the preferred assembly line shown in FIG. 1, the wound core is cut by a pinch cut device which is described and claimed in application Ser. No. 126,543 for Method of Cutting Wound Magnetic Cores, filed July 25, 1961, now Patent No. 3,160,044, in the name of the present inventor and assigned to the same assignee as this invention. The operation of the cutting mechanism 30 is thoroughly described in the aforesaid application and will not be described in detail herein. However, as can be seen from FIG. 1, the wound core, designated 32, is placed upon the anvil 34 of the cutting mechanism 30. The outer strip 36 of the core 32 is pulled away from the blade 38 so as not to be cut thereby and then, in the manner described in the aforementioned application Ser. No. 126,543; the blade mechanism 38 is driven through the core material 12 thereby cutting each of the laminations of core 32. In the form of invention described herein, the lowermost lamination 40 is not cut by blade 38 for a reason which will be hereinafter more fully discussed.

After the core 32 has been severed by the cutting mechanism 30 it may be removed to a weighing scale 42 where the core is weighed to determine that it meets the desired requirements of the electromagnetic apparatus for which it has been designed. As will be understood, in an assembly line operation, only occasional cores will be weighed, to check the correctness of the winding operation. After the core 32 has been weighed or after it is removed from the cutting mechanism 30, if it isnot weighed, the inner and outer lamina tions 40 and 36, respectively, are separated from core 32. The remaining laminations of core 32 are then placed in an expanding mechanism, indicated at 44. In mechanism 44 a pair of driven horns 46 are inserted into the opening of core 32 and are then moved apart by means of an air motor, electric motor, or any other desired mechanism, so as to open the core as shown in FIG. 1. After the core has been expanded the core 32 is then clamped and, by means of such clamp (not shown), it is placed on a separating mechanism 48, where each of the various laminations of the core is separated so as to provide the desired staggered joints in the various lami nations. The separator mechanism is operated to separate each separate lamination and to move it with reference to its adjacent lamination so as to provide the staggered joints which are desired. In the preferred embodiment, usually a packet of laminations are separated, the packet containing any desired number of laminations. In FIG. 1, the separator 48 is shown in the form of a separator which is described and claimed in application Ser. No. 227,152, filed concurrently herewith, now Patent No. 3,113,- 375, for Mechanism for Separating Core iLaminations, in the names of Gareth G. Somerville and Aldo C. Blasioli, and assigned to the same assignee as this invention. Reference may be made to such application for a more complete description of the separator 48. Of

course, it will be understood that any type of separator mechanism, either automatic or manual may be used in the method of this invention, as desired. As each lamination is separated from the core it is shifted, and after a sufficient number to make the packet have been separated from the main core 32 they are removed from the separator 48 and placed in a core stacking machine 50.

The inner layer 40, which was first removed, is wrapped about a dummy mandrel 52 of the core stacking machine 50. Due to the pre-set or pre-curl, which has been placed into the magnetic material 12, the inner lamination 40 tends to wrap about the dummy mandrel 52. The first packet of separated laminations is then placed about the inner layer 40, and due to its pre-curl, tends to tightly surround the inner lamination 40. As each of the packets is separated by separator 48 it is assembled onto the core stacker 50; generally with its staggered joints being placed such that the first joint of the packet is approximately in line with the first joint of the proceeding packet. In order to tightly close the joints in each of the various laminations, the laminations being butted upon themselves in the separation from the separator 48, the core stacker 50 is provided with clamping means, indicated at 54, which tend to squeeze the core in its circular shape thereby closing tightly each of the joints formed in the separate laminations. After the entire core 32 has been separated into packets by separator 48 and formed onto the core stacker 50, with the various core joints being staggered with respect to adjacent core joints, the outer lamination 36, which was first removed from the core, is then wrapped about the exterior of the core device of the core 32. The outer lamination is usually spot welded, as by welding means 55, before forming into the desired shape. Of course, the core 32 could be handed, rather than welded, if desired.

After the core has been re-assembled, in the core stacker device 50 and the final lamination 35 has been wrapped there around, and welded or banded, the core is removed from the core stacker 50 and is placed in a forming mechanism 56. The mechanism 56 shapes the core 32 in the desired, predetermined shape. In FIG. 1, one such shape is indicated as a substantially rectangular core having curved corners. After the core has been shaped as desired by the forming mechanism 56 the core is clamped in such shape, as is well understood by those skilled in this art. The shaped, clamped core is then placed upon an annealing sheet 58. When a sufficient number of cores are placed thereon the cores are then moved to an annealing furnace to be provided with the stress anneal or the grain growth anneal, as necessary, in a manner which is well understood by those skilled in the art.

From the above description of the preferred embodiment of this invention which is disclosed in the assembly line setup of FIG. 1, the method of this invention will be readily understood. As will be clear to those skilled in the art, in order to provide a series of butt joints in the spirally wound core 32 it is necessary that the inner lamination and the outer lamination be removed prior to the separating of the remaining laminations in the separator 48. This will enable each of the laminations of the remaining core 32 to be separated so as to provide a series of butt joints in each of the separate packets. Further, it will be clear that where the desired shape of the core is circular, that the core may be moved directly from stacker 5% to the annealing sheet 58.

FIGURE 2 and FIGURE 3 show a pre-formed, single turn, cut core in the semi-finished and in the finished state, made according to the preferred method of this invention. As shown particularly in FIG. 2, the core 32 is shown as it is finally stacked in the core stacking mechanism 50 of FIG. 1. As can be seen from FIG. 2, the inner layer of the core 32 comprises a lapped lamination which overlaps itself approximately one-quarter of a turn. The inclosed laminations of the core 32 between the inner lamination 40 and the outer lamination 36 are shown as comprising ten laminations which are buttjointed, as shown by the butt joint 60 in lamination 62, which is adjacent to the inner lamination 40. As can be seen, each of the butt joints are staggered across the top of the core 32 to form two packets, each of the packets comprising five laminations with the butt joints of each packet being staggered across the top of the core 32, and each series of five butt joints being approximately in line with the comparable butt joint of the other packet. Of course, it will be understood that core 32 may contain any number of laminations and packets as desired or necessary, for a particular apparatus. The outer lamination 36 is shown as being wrapped about the outer portion of core 32 and overlaps itself, in the same manner as discussed with reference to lamination 40. As can be seen, both with reference to lamination 40 and lamination 36, where the laminations overlap an opening 64 adjacent lamination 40 and 66 adjacent lamination 36 is formed, since the magnetic material does not wholly conform to the adjacent lamination in the vicinity of the inner end of the overlapped laminations. Of course, it will be understood, that the thickness of the strip material forming the laminations will determine the size of the openings 64 and 66. When very thin material is used, such as 12 mil strip, the openings 64 and 66 are hardly discernible.

After the laminations have been re-stacked in the manner shown in FIG. 2 to provide the staggered butt joints, with each of the butt joints in the various packets being substantially aligned with similar butt joints in adjacent packets, the core 32 is then placed in the forming machine 56 and formed into the desired shape. As was shown in FIG. 1, in this instanw the shape is that of a rectangular core having rounded corners. FIGURE 3 shows a top view of the completely formed rectangular core as it is placed upon the annealing plate 58 prior to annealing of the core. The clamps which are used to hold the core in shape are not shown. As can be seen from FIG. 3, the inner lamination 40 is formed in a rectangular manner with the overlapping edges of the inner layer 40 on both the top and the bottom winding leg. The outer lamination 36 has its overlapped ends in the yoke of the core 32, although the overlap could be in a winding leg, if desired. As will be noted from FIG. 3, in the forming of :core 32 from the round shape to the rectangular shape an additional shifting of the various butt joints occurs such that after the core has been formed in its rectangular shape, none of the butt joints in the various packets are aligned with the butt joints in the other packet. Thus, it can be seen, that by making each of the joints a butt joint in all of the inclosed laminations of the core formed according to the method of this invention, that the various joints in the lamination are staggered in a random manner such that essentially none of the various butt joints are aligned with any butt joints in any other lamination of the core. Thus, it can be seen, that by this method the core is provided with staggered joints with none of the butt joints being aligned with any of the other butt joints in the core.

While a preferred assembly line has been shown for making a single turn, pre-formed core according to the method of this invention, it will be understood that various changes can be made in the items of the assembly line, if desired. Further, it should be understood that it is not essential to the method of this invention that the inner and outer layers or laminations of the pre-forrned core be overlapped, in the manner shown in FIGS. 2 and 3. If desired, as Will be understood, these laminations can be dispensed with and the core may be formed only of the butt joint laminations. Also, as will be understood, the pre-formed core could be of any desired shape, including circular, if desired. Thus, while there has been shown and described the present preferred method of making this invention and an assembly line of apparatus for making the core of this invention, it will be understood that various changes may be made without departing from the spirit and scope of the invention as set forth in the claims appended hereto.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A method of making a pre-formed, single turn magnetic core comprising the steps of pre-curling a strip of magnetic material, winding said pre-curled strip of mag-.

netic material upon a winding mandrel to form a spirally wound magnetic core, cutting said spirally Wound magnetic core along a single plane, expanding said magnetic core to open it along said cutting plane, separating the laminations into packets with staggered joints in each of said packets, stacking said packets in a core for-m with the joints in one packet being aligned with similar joints of the other packets, forming the stacked core to the desired shape and annealing said core to relieve the stresses built up on the core material during the winding, cutting and forming steps.

2. A method of making a pre-formed single turn magnetic core comprising the steps of pre-curling a strip of magnetic material, winding said strip of magnetic material on a winding mandrel to provide a spirally wound magnetic core, cutting said magnetic core along a .single plane, expanding said magnetic core along said out plane, separating the laminations of said cut magnetic core into a number of packets each packet having their joints staggered with respect to each other, stacking the staggered joint packets in a core form with the joints in one packet being aligned with the joints of the other packets, forming said wound core into its desired shape, the forming of the core causing the various joints in the packets to become misaligned with respect to the joints in the other packets, thereby providing for a core having random joints and finally annealing said core so as to relieve the stresses formed in the core during the cutting, winding and forming steps.

3. A method of making a pre-formed magnetic core comprising the steps of removing a strip of magnetic material from a payoff reel, de-burring the edges of said strip material, pro-curling said strip material, winding said pre-curled material on a Winding mandrel to form a spirally 'WOIJIId magnetic core, cutting said spirally wound magnetic core along a single plane, expanding said cut magnetic core along said cutting plane, separating the laminations of said cut core into packets with the joints in each packet being staggered with respect to each other, stacking the packets in a core form with the joints of one packet being aligned with the joints of the next packet, forming the core to a desired shape whereby the aligned joints are disrupted and the core is provided with random joints, and annealing said core to relieve the stresses built up during the winding, cutting and forming steps.

References Cited UNITED STATES PATENTS 2,260,398 10/1941 Otte 336213 2,771,664 11/1956 Duenke 29155.57 3,025,483 3/1962 Treanor 336213 3,027,628 4/1962 Wilk et al. 29155.57 3,107,415 10/1963 Ellis 29-15557 XR 3,200,476 8/1965 Olsen et .al. 29155.57

JOHN F. CAMPBELL, Primary Examiner.

JOHN T. BURUS, Examiner.

W. ASBURY, R. W. CHURCH, J. CLINE,

Assistant Examiners. 

1. A METHOD OF MAKING A PRE-FORMED, SINGLE TURN MAGNETIC CORE COMPRISING THE STEPS OF PRE-CURLING A STRIP OF MAGNETIC MATERIAL, WINDING SAID PRE-CURLED STRIP OF MAGNETIC MATERIAL UPON A WINDING MANDREL TO FORM A SPIRALLY WOUND MAGNETIC CORE, CUTTING SAID SPIRALLY WOUND MAGNETIC CORE ALONG A SINGLE PLANE, EXPANDING SAID MAGNETIC CORE TO OPEN IT ALONG SAID CUTTING PLANE, SEPARATING THE LAMINATIONS INTO PACKETS WITH STAGGERED JOINTS IN EACH OF SAID PACKETS, STACKING SAID PACKETS IN A CORE FORM WITH THE JOINTS IN ONE PACKET BEING ALIGNED WITH SIMILAR JOINTS OF THE OTHER PACKETS, FORMING THE STACKED CORE TO THE DESIRED SHAPE AND ANNEALING SAID CORE TO RELIEVE THE STRESSES BUILT UP ON THE CORE MATERIAL DURING THE WINDING, CUTTING AND FORMING STEPS. 